IMAGhttp://physionet.org/Linux, Mac OS X, Cygwin/Windows, Solaris, other UNIX/POSIX platformsPhysioNetYesgeorge@mit.eduGNU General Public License (GPL)George MoodyPhysioNet offers free access via the web to large collections of recorded physiologic signals (PhysioBank) and related open-source software (PhysioToolkit). The PhysioNet Resource, established in 1999, is intended to stimulate current research and new investigations in the study of complex biomedical and physiologic signals.PhysioBank is a large and growing archive of well-characterized digital recordings of physiologic signals, time series, and related data for use by the biomedical research community. PhysioBank currently includes more than 50 collections of cardiopulmonary, neural, and other biomedical signals from healthy subjects and patients with a variety of conditions with major public health implications, including sudden cardiac death, congestive heart failure, epilepsy, gait disorders, sleep apnea, and aging. These collections include data from a wide range of studies, as developed and contributed by members of the research community.PhysioToolkit is a large and growing library of software for physiologic signal processing and analysis, detection of physiologically significant events using both classical techniques and novel methods based on statistical physics and nonlinear dynamics, interactive display and characterization of signals, creation of new databases, simulation of physiologic and other signals, quantitative evaluation and comparison of analysis methods, and analysis of nonequilibrium and nonstationary processes. A unifying theme of many of the research projects that contribute software to PhysioToolkit is the extraction of ``hidden'' information from biomedical signals, information that may have diagnostic or prognostic value in medicine, or explanatory or predictive power in basic research. All PhysioToolkit software is available in source form under the GNU General Public License (GPL).The PhysioNet library provides a wide range of tutorial and reference materials to provide researchers and students with the information needed to make use of PhysioBank data and PhysioToolkit software.PhysioNetWorks provides a virtual laboratory where researchers can work together with the PhysioNet team and with colleagues anywhere in the world to create, evaluate, improve, document, and prepare new data and software "works" for publication on PhysioNet. PhysioNet Works provides reliable web-accessible backup, tools for viewing and annotating data interactively, and an active community of researchers who can help by annotating, analyzing, and reviewing data, and by contributing additional relevant data.In cooperation with the annual Computing in Cardiology conference, PhysioNet hosts a series of challenges, in which researchers and students address unsolved problems of clinical or basic scientific interest using data and software provided by PhysioNet. AvailableHarvard-MIT Division of Health Sciences and TechnologyYesGeorge Moody